1. Field of the Invention
The present invention relates to wireless communication systems and to a system and method for measuring signal to noise ratios for a multi-modulation burst modem.
2. Description of the Related Art
A wireless communication system facilitates two-way communication between a plurality of subscriber radio stations or subscriber units (fixed and portable) and a fixed network infrastructure. Exemplary communication systems include mobile cellular telephone systems, personal communication systems (“PCS”), and cordless telephones. The key objective of these wireless communication systems is to provide communication channels on demand between the plurality of subscriber units and their respective base stations in order to connect a subscriber unit user with the fixed network infrastructure (usually a wire-line system). In the wireless systems having multiple access schemes, a time “frame” is used as the basic information transmission unit. Each frame is sub-divided into a plurality of time slots. Some time slots are allocated for control purposes and some for information transfer. Subscriber units typically communicate with their respective base station using a “duplexing” scheme thus allowing for the exchange of information in both directions of the connection.
Transmissions from the base station to the subscriber units are commonly referred to as “downlink” transmissions. Transmissions from the subscriber units to the base station are commonly referred to as “uplink” transmissions. Depending upon the design criteria of a given system, wireless communication systems have typically used either time division duplexing (“TDD”) or frequency division duplexing (“FDD”) methods to facilitate the exchange of information between the base station and the subscriber units.
Multiple techniques are available for modulating and demodulating the transmitted signal in a wireless communication system. These modulation techniques vary in their robustness. Typically, a more robust modulation technique has a lower transfer bit rate. However, information modulated with such a technique will be less prone to generating errors when demodulated at the receiving site due to adverse environmental conditions along the signal's path. A wireless communication system operates with both of these competing interests in mind.
Wireless communication systems perform some form of signal quality or error measurement on a received signal. These measurements often monitor changes in the environment between the subscriber unit and base station. These changes can impact a subscriber's quality of service. Based on these measurements, the wireless communication system can adapt its modulation technique for the changing conditions. However, these measurements may not be available to the subscriber unit. Without continual measurements, the subscriber unit is unable to stay abreast of environmental conditions which may subsequently impact its quality of service.